The feud began after Sheen and then-fiancée Brett Rossi saw the R&B songstress at a restaurant where they were dining. Sheen later explained on Twitter that he had sent a request to the "Work" singer's table asking if he could introduce his now-ex to Rihanna, but she refused, claiming there were too many paparazzi outside.

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Rossi walked away hurt and Sheen went on a Twitter tirade, noting how he always makes time for fans and encouraged Rihanna to do the same.

"See ya on the way down...and actually, it was a pleasure NOT meeting you. Clearly we have NOTHING in common when it comes to respect for those who've gone before you," he wrote. "I'm guessing you needed those precious 84 seconds to situate that bad wig before you left the restaurant."

Sheen concluded by sharing his advice for the "Pour It Up" signer: "Here's a tip from a real vet of this terrain; If ya don't wanna get bothered DONT LEAVE YOUR HOUSE! and if this 'Prison of Fame' is soooooooo unnerving and difficult, then QUIT, junior! c #Hamateur."

Rihanna responded by changing her Twitter banner to a picture of her autographing a fan's sign, but Sheen's head was superimposed on the body.

The Two and a Half Men alum didn't stop with Rihanna. Sheen also insulted Ferris Bueller's Day Off co-star Jennifer Grey after Cohen played a clip from the iconic movie.